Acoustic type folding door



D. C. HOLLOWAY ACOUSTIC TYPE FOLDING DOOR Dec. 14, 1965 3 Sheets-Sheet 1 Filed Dec. 17, 1964 It: J '1 m I z m M? H. W. llli; 2 .I. I H 1 E W M m m n w u 1 T w H n M Inventor ll] IL.

Don. C. flollowag/ 85/ Maw,

Dec. 14,1965 D. c. HOLLOWAY ACOUSTIC TYPE FOLDING DOOR 3 Sheets-Sheet 2 Filed Dec. 17, 1964 I121! eni'or Don C. j'follo wald fi-ttorrzegs 55, Mm, 6mm

Dec. 14, 1965 D. c. HOLLOWAY ACOUSTIC TYPE FOLDING DOOR Filed Dec. 17, 1964 3 Sheets-Sheet 5 Inventor Don. C. HoHoWcHd/ 135 Mm, m Z MJIZIIMM zFH' -ornegs Patented Dec. 14, 1%65 ice 3,223,147 ACOUSTIC TYPE FOLDING DOOR Don C. Hoiioway, Janesvilie, Wis., assignor to Hough Manufacturing Corporation, a corporation of Connecticut Filed Dec. 17, 1964, Ser. No. 421,747 7 filaims. (Cl. 160-84) This application is filed as a continuation-in-part of pending application Serial No. 285,666, filed June 5, 1963.

This invention relates to accordion type folding doors and particularly to such doors that are intended when closed to serve as sound insulating or sound retarding means.

Accordion folded doors have found a wide market as a means for separating large rooms such as class rooms into two or more smaller rooms, and in such use the effectiveness of such accordion folding doors as a sound barrier has become increasingly important. Attainment of a high degree of efiiciency of such doors insofar as sound insulation may be concerned has however been extremely difiicult to attain because of the fact that such doors, when they are in their open or collapsed relation, must occupy a relatively small portion of the opening that is to be closed by such doors. This is usually termed the stacking ratio, so that a door that may be collapsed to a dimension equal to of its extended or closed dimension is said to have a stacking ratio of Such a stacking ratio of is generally considered to be satisfactory, but it has been found that in efforts to increase the sound reduction or sound barrier capabilities of such accordion folding doors, there has in most instances been a marked increase in the stacking ratio which limits the utility of such doors.

Accordion folding doors of the kind of which the present invention relates are provided basically by a pair of vertical end posts connected by lazytongs at their opposite ends to the end posts near the upper and lower end posts, at least one of the end posts, and one or more intermediate points of the upper lazytongs being suspended from roller carriages that ride in an overhead track that extends across the opening that is to be closed by the door.

On opposite sides of the lazytongs it has been the practice to suspend foldable covers so that the door may be extended or collapsed with the foldable outer covers providing a continuous and impervious surface on each side of the door. It has further been the practice to provide for an effectual air seal at each of the end posts with respect to the door jambs or with respect to the end post of a cooperating door where two collapsible doors cooperate in closing a particular opening or door. The upper and lower edges of the covers are normally spaced a short distance from the top of the door opening and from the floor, and flexible sweep strips are customarily provided along the upper and lower edges of both of the covers so that an effectual air seal is provided along the top and bottom edges of both of the covers. This air sealing along the end posts and the top and bottom edges of the covers has served to block direct transmission of sound through air leakage paths in the door structure when it is closed, but over and above the air sealing arrangements that have heretofore been used, efforts have been made to further reduce the sound transmission through the provision of means mounted internally of the door, or in other Words between the two outer covers.

Such internal means have taken different forms, and in early work in this art, a continuous blanket of a fibrous material such as Fiberglas was used just inside of the outer covers of the doors. This proposal, however, failed to meet the needs of the art because of the substantial increase in the stacking ratio of such doors, and because of this, and because the sound reduction has been relatively slight, the use of the continuous blanket of sound absorbent material inside of each of the covers and in some instances fastened directly to such covers, has not met with success.

In an eifort to attain the desired degree of sound reduction while at the same time retaining a favorable stacking ratio in the doors, the doors have heretofore been provided with foldable means located within the door and designed to impart substantial mass to the door. Thus in Merrill Patent No. 2,903,055, two foldable internal structures were provided that were carried by the lazytongs and which embodied elongated vertical panels made from material such as chipboard and pivoted together along their vertical edges. The structure shown in the Merrill Patent, when coupled with an effective air seal about the edges of the door, did obtain a slight degree of added sound reduction, but as the demands of architects and designers have become more and more exacting, even such structures fail, in many instances, to bring about the desired degree of noise reduction.

In view of the foregoing it is the primary object of the present invention to provide an accordion door wherein extremely high coefficients of noise reduction are attained while at the same time retaining a favorable stacking ratio in the door. Other and more specific objects of the invention are to secure such improved acoustic performance in accordion doors without requiring addition of undue mass to the door, and to accomplish this in a way that does not materially complicate the manufacture and assembly of the doors.

Other and further objects of the present invention will be apparent from the following description and claims, and are illustrated in the accompanying drawings, which, by Way of illustration, show preferred embodiments of the present invention and the principles thereof, and what is now considered to be the best mode in which to apply these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired by those skilled in the art without departing from the invention.

In the drawings:

FIG. 1 is a perspective view showing accordion folding doors of this invention installed as room dividers for dividing a large room into two or more small rooms;

FIG. 2 is a schematic exploded perspective view illustrating the basic elements of the folding doors;

FIG. 3 is an enlarged horizontal cross section through a folding door embodying the invention;

FIG. 4 is an enlarged horizontal cross sectional view through one of the covers of the door;

FIG. 5 is a view similar to FIG. 4 and showing further details of construction;

FIG. 6 is a view similar to FIG. 5 but showing an alternative embodiment of the invention;

FIG. 7 is a fragmentary vertical sectional view showing the sweep strips in association with the door cover;

FIG. 8 is a view similar to FIG. 3 and showing the alternative cover structure of FIG. 6;

FIG. 9 is an enlarged horizontal cross sectional View of one of the covers;

FIG. 10 is a horizontal cross sectional view showing a portion of one cover in its folded relationship that it assumes when the door is open;

FIG. 11 is a fragmentary vertical sectional view showing the sweep strip in position on the upper edge of the cover shown in FIG. 9; and

FIG. 12 is an enlarged view of the sweep strip that is used.

For purposes of disclosure the invention is herein illustrated as embodied in acoustic folding doors 20 that are mounted as shown in FIG. 1 in a large room so that the doors may be opened when the entire area of the room is to be utilized for one meeting room or class room and so that by closure of the folding doors 20, the main room may be subdivided into a plurality of smaller rooms. In the present instance the main room is partially divided by cross walls 21 having doors 22 therein and each door has a head 22H and jamb 22]. As to each door 22, two accordion folding doors 26 are utilized because of the relatively large horizontal dimensions of the openings 20, and it will be recognized of course that a single folding door 2% might in many instances be used in accordance with conventional practice.

The accordion folding doors 20 that are herein illustrated, and in which the .present invention has been embodied, are of the general kind illustrated in several prior patents owned by the assignee of the present application, and as the description proceeds, particular attention will be directed to such prior patents for purposes of reference.

Thus the folding doors 20 shown herein are of the general kind illustrated in Johnson et al. 3,056,193, patented October 2, 1962, and each such door comprises a main frame having a pair of vertical edge posts 24 and 25 at opposite ends thereof and interconnected by upper and lower lazytongs structures 26U and 26L. The end post 24 is located at one jamb 221 of the opening and is secured thereto in fixed and air sealed relation, while the other or lead post 25 is suspended movably from an overhead track 27 that is extended across the head 22H of the door opening. Such suspension is provided by a wheeled carriage 25C that rides in the track 27, and because of the relatively great extended length of the lazytongs the upper lazytongs 26U is similarly supported from the track 27 by wheeled hangers 28 that are shown in FIG. 2. The details of the end posts 24 and 25, the lazytongs, and the wheeled hangers 25S and 28 may be in accordance with the teachings of the aforesaid Johnson et a1. patent.

The end post 24 and 25 together with the interconnecting lazytongs 26U and 26L serve as an extensible inner frame for the door 20, and on opposite sides of this extensible frame, foldable sound barriers are provided which in the present instance take the form of covers 30 that are detachably secured on the frame in the manner disclosed in the aforesaid I ohnson et al patent. Broadly considered, it may be pointed out that the lazytongs 26U and 26L have a plurality of pivotal joints between the links thereof, and that the uppermost row of such pivotal joints is provided by a plurality of projecting support pins 31 which provide a part of the detachable connection between the covers 30 and the lazytongs.

The particular way in which the covers 30 are connected in this instance to the support pins 31 is related to the particular structure of the covers 30 that are employed in the present instance. Thus, it may be pointed out that each cover 30 comprises a plurality of alternate wide slats 33 and narrow slats 34- that are pivotally interconnected by inner and outer cover sheets 55 and 56 as will be described in further detail hereinafter.

At the opposite ends of each cover, attachments slats 37 are provided that engage opposite sides of the respective end-posts and are secured thereto in the manner described in'the aforesaid Johnson et a1 patent.

In a typical door arrangement the wide slats are more than five times as wide as the narrow slats. Thus, the wide slats 33 may be 2 /3 inches wide and the narrow slats 34 may be inch wide, and the spacing between slats may be inch.

While the details of the covers 30 will be described hereinafter, it may be here .pointed out that along the upper and lower edges of these covers, flexible sweep strips 40 are provided in accordance. with usual practice in acoustic doors and these sweep strips 40 ride along the ceiling or opposed face of the upper and lower edges of both of the covers 30. The sweep strips 40 as shown 4 in FIGS. 11 and 12 are of five-ply construction with the center ply being provided by a felt member 40F.

Means are conventionally provided for sealing the lead post 25 of the door 20 with respect to the lead post of the associated door 20, it being noted of course that in the event that a single folding door 20 is employed in a particular door opening, the opposed element of this sealing couple is mounted in opposed and sealed relation with respect to the jamb of the door opening. In the present instance this sealing action is provided by a face member secured to the lead post 25 of one of the two cooperating doors 20, and an opposed face member 71 is secured to the lead post 25 of the other door 20. The face member 74 has a pair of spaced ferrous metal strips 72 in its leading face and near opposite sides thereof, while the other sealing element 71 has a pair of elongated sealing elements 73 mounted therein so as to be located opposite the ferrous element 72. The sealing elements 73 are of a known type wherein a bendable plastic strip has permanent magnet means embedded therein so that when the two members 70 and 71 are located adjacent to each other, the magnet members attached themselves to the respective ferrous strips 72 to form an effective seal between the members 76 and '71 throughout the entire vertical length of these members. A latch or lock 74 is preferably provided'to act between the lead post 25 and the member 72, and this latch may be of the kind shown in Ensign Patent No. 2,861,660, patented November 22, 1958.

The structures thus described provide an accordion folding door that has covers on opposite sides thereof and in which the edges of both covers are effectually sealed against air leakage about all four of the edges thereof. This air sealing of the covers about the four edges thereof provides an effectual sound barrier particularly with respect to sound of a relatively high frequency, but in practice it is found that in the lower or middle ranges of sound as encountered in ordinary school rooms or meeting rooms, it is highly desirable to provide for additional attenuation of the sound, and it is in this respect that the present invention has achieved most unexpected and highly desirable results.

In experimental studies of the sound transmission characteristics of accordion folding doors of the general kind hereinabove described, I have reviewed the general and accepted procedures in the art with the idea of determining the validity thereof. Over and above the employment of an effective seal about the four edges of such a door, the basic concept that has been accepted in this field has been that by adding more and more mass to the door it is possible to further increase the sound attenuating properties of the door. In testing this theory it has been determined that while addition of mass to such a door has an appreciable effect in giving the door better sound attenuating characteristics, the manner in which the mass is provided in the door also has a significant influence on the problem.

In my studies of the problem, it has become apparent that one of the major factors in producing sound transmission through the door is provided by the mechanical vibrating action of the sound barrier which absorbs the sound energy on one side so as to be set in vibration, thus to provide a sound source which creates sound between the two covers, and by the same action on the cover or sound barrier at the other side of the door, causes the creation of sound in the room on the opposite side of the door.

Under and in accordance with the present invention, the folding sound barriers on opposite sides of the folding frame structure have added mass imparted thereto in such a way as to minimize vibration of the panel elements thereof, and means are associated with such panel elements to minimize sound emission from the inner surfaces thereof and to absorb any sound between these sound barriers so that it is ineffective to initiate appreciable sound-creating vibration of the sound barrier on the opposite side of the door. As a further and more specific feature of the invention, the outer covers of the door have themselves been utilized as to the location of the added mass and as the carrier for the means that minimize sound emission and absorption of sound within the door. Through such procedures, the sound attenuating properties of the doors have been increased to a startling ex tent while at the same time minimizing the amount of mass or weight added to the door. Furthermore, these results are accomplished, as will be explained, without adversely affecting the stacking ratio of the doors.

Thus as will be evident in FIGS. 3 to 6, the wide slats 33 of each cover are disclosed as multi-ply structures and are formed to include a thin plate 50 of mild or rolled steel which preferably is of 24 gauge thickness, although thicknesses from 22 gauge to 30 gauge have been employed. The steel plate 50 is initially somewhat wider than the final width that is to be provided in the slat 33, and a thin panel 51 of chipboard is adhered to one face of the steel strip 50, and the vertical edges of the steel strip are rolled into returned bends or flanges 53 which clamp the chipboard panel 51 at its edges and serve also to impart stiffness to the steel plate 50. A second chipboard panel 54 is then adhered to the flanges 53 and the panel 51 so that the panel 54 overlies the flanges 53 as will be evident in FIGS. 4 and 5. The successive wide slats 33 and the alternate narrow slats 34 and 348 are then connected together in a pivoted relationship by the application of a continuous decorative outer cover sheet 55, of vinyl plastic or the like, and an inner cover sheet 56 that may be made of a substantial grade of kraft paper. Intermediate the wide and narrow slats, the inner and outer cover sheets 55 and 56 are adhered together to form flexible hinges 57. The narrow slats 34 and 348 may be formed, as described in the aforesaid Johnson et al. patent, from cardboard or chipboard or the like.

On the inner surface of the wide slats 33, vertically extending panels 60 of a resilient fibrous insulating material such as matted glass fibers and glued to the cover sheet 56, and as shown in FIGS. 3 to 5, this glass fiber panel is of a width sligthly less than the width of the Wide slats 33. The glass fiber panel 6% is preferably located relatively close to one edge of the wide slat 33 and is spaced somewhat from the edge of the slat that is connected to the mounting or supporting slats 348. In particular, the wide slats 33 are provided with matted glass fiber panels 60 of /2 inch thickness when uncompressed, and these panels are of a material of a density of /2 pound per cubic foot.

In the form of the invention just described, the stiffness of the Wide slats 33 is attained by the reverse bends 53 on the metal layer 50. In the form of the invention shown in FIGS. 6 and 8 to 10, the desired stiffening is attained in a different manner. Thus the wide slats in FIGS. 6 and 8 to have been identified as slats 133, the internal portion of which is provided by a steel plate 150 and a cardboard or chipboard layer 151 that is adhesively secured thereto. It is the assembly formed by the members d and 151 that is faced in this instance on opposite surfaces thereof by the outer and inner cover sheets 55 and 56 in the manner hereinbefore described. In the form shown in FIGS. 6 and 8 to 10, the stiffening of the wide slat assembly is provided by bending the metal slat and the chipboard slat to a slight angle along a longitudinal line at or close to the transverse center line of the slat. In the present instance the included angle between opposite sides or side portions of the slat is about 180 and it is found that this imparts substantial stiffness to the wide slat 133.

On the inner surfaces of the wide slats 133, fibrous insulating pads 60 are adhesively secured in the manner and relationship hereinbefore described.

In both of the forms of the invention that have been described, the fibrous insulating pads 60 are carried on the wide slats in such a way that when the door is open, the

insulating pads 60 are slightly compressed in the manner shown in FIGS. 6 and 10, and it has been found that such insulating pad 60 may be compressed to about one-half their original thickness and will nevertheless return to their original volume or thickness when the door is moved into its closed position. With this arrangement, the pivoting action of the slats of the covers of the door is not in any way modified, nor is the stacking ratio of the door increased. Hence, the sound insulating action of the fibrous pads 60 is attained while at the same time maintaining the desirable stacking ratio that would normally be attained by such a door without the fibrous pads.

The acoustic performance rating of folding doors of this kind is based on standardized test measurements of the sound transmission loss at different frequencies between 125 and 4000 cycles per second, with the results being expressed as a rating in decibels that constitutes the average attenuation for the several frequencies measured. This rating in decibels corresponds with a newly adopted standard for measuring sound transmission loss ASTM E61T under which the rating is designated as the Sound Transmission Class, or STC of such door.

Tests of the acoustic door of this invention have shown that the structural features of this door make possible attainment of STC ratings that were heretofore unattainable in doors that possess satisfactory weight and folding or stacking characteristics. Thus, it has been determined that a flat steel ply included in the slats increases the STC rating from 5 to 8 points according to the thickness or weight between 30 gauge and 22 gauge, while bending of the steel ply, as shown in FIG. 5 or in FIG. 6, so as to stiffen the structure, results in an improvement of approximately 2 SRC points without addition of further weight or mass. The stiffened steel-containing slats thus contribute from 7 to 10 points toward improvement of the STC rating of the doors of this invention.

Keeping in mind that it is highly desirable where possible to minimize the Weight of doors of this character, it should be observed that over and above an average weight of about 1.7 pounds per square foot that is required in the folding door of the aforesaid Johnson et al. patent, the provision of a 30 gauge steel ply in the slats brings this average weight up to about 3 pounds per square foot, a 24 gauge plate produces a weight of about 3.6 pounds per square foot, while a 22 gauge plate produces a weight of about 4.3 pounds per square foot in the door. The fibrous pads 60 however enable substantial acoustic improvement to be attained with the addition of relatively little weight, such pads in /1 inch thickness contributing from 7 to 9 STC points while adding but 0.4 pound per square foot to the Weight of the door.

Thus, the fibrous pads 60, on the basis of weight contribute greatly to the improvement of the acoustic properties of the door, but because of the physical characteristics of the door, the very volume of the fibrous material constitutes a serious limitation as to extent to which it may be utilized in such doors. However, it has been found that where stiffened steel plates and individual fibrous sound insulating pads are employed in the manner described, the resulting folding doors have an extremely favorable stacking ratio of less than and attain an STC rating far above that obtained with prior door structures of this general type. As an example, a door structure with the stiffened plate structure, of FIG. 5, made from 28 gauge material, or with the plate of FIG. 6 made from 24 gauge material, and with fibrous pads as described, the resulting doors have been found, in a properly sealed installation, to attain an STC rating of 40. It should be noted that this rating exceeds the rating of the conventional concrete block wall.

From the foregoing description it will be apparent that the present invention provides an accordion folding door that attains an extremely high noise or sound attenuation rating and this rating is attained while at the same time maintaining favorable stacking ratio in the door. It will 7 also be apparent that this secures greatly improved acoustic performance in accordion folding doors without requiring addition of undue mass to the doors, and is accomplished in such a way that the manufacture and assembly of the doors is not unduly complicated.

Thus, while preferred embodiments of the invention have been illustrated herein, it is to be understood that changes and variations may be made by those skilled in the art without departing from the spirit and scope of the appended claims.

What is claimed is:

1. In an accordion type folding door having a pair of end posts that define opposite vertical end edges of the door, upper and lower extensible and collapsible lazytongs connecting said posts, foldable cover means disposed along opposite sides of said lazytongs and connected at opposite ends to the respective posts, flexible sealing skirts attached to and projecting from the upper and lower edges of the cover means, each cover means including a plurality of vertically elongated closely side-by-side disposed relatively wide and relatively narrow slats alternately arranged and pivoted together by means including inner and outer flexible sheets adhered to opposite faces of each of the slats, means securing every other one of said narrow slats to intermediate points of each lazytongs, each of said wide slats being a substantially flat sheet-like structure, and vertically extended pads of low density resiliently compressible fibrous sound insulating material mounted exteriorly in full surfaced flush contacting relation against the inner cover sheets at locations overlying and substantially masking the wide slats, said pads being of a thickness somewhat greater than one half the width of the narrow slats to increase the frequency sound isolating characteristics of the door by at least 4 db and to undergo yieldable compression when the door is folded to maintain substantially the same stacking ratio.

2. An arrangement in accordance with claim 1 andv wherein said pads are /2 inch thick and of a density of /2 pound per cubic foot to increase the frequency averaged sound isolating characteristics of the door by about 7 db while maintaining substantially the same stacking ratio.

3. In an accordion type folding door having a pair of end posts that define opposite vertical end edges of the door, upper and lower extensible and collapsible lazytongs connecting said posts, foldable cover means disposed along opposite sides of said lazytongs and connected at opposite ends to the respective posts, flexible sealing skirts attached to and projecting from the upper and lower edges of the cover means, each cover means including a plurality of vertically elongated closely side-by-side disposed relatively wide and relatively narrow slats alternately arranged and pivoted together by means including inner and outer flexible sheets adhered to opposite faces of each of the slats, and means securing every other one of said narrow slats to intermediate points of each lazytongs, each of said wide slats being a substantially fiat sheet-like multi-ply structure and comprised of one layer of thin walled sheet steel stock provided with a full height bent portion to increase the anti-vibration rigidity of the wide slats and increase the frequency averaged sound isolating characteristic of the entire door.

4. An arrangement in accordance with claim 3 and including vertically extended pads of sound insulating material mounted exteriorly in full surfaced flush contacting relation against the inner cover sheets at locations overlying and substantially masking the wide slats.

5. In an accordion type folding door having a pair of end posts that define opposite vertical end edges of the door, upper and lower extensible and collapsible lazytongs connecting said posts, foldable cover means disposed 'along opposite sides of said attached to and projecting from the upper and lower edges of the cover means, each cover means including a plurality of vertically elongated closely side-byside disposed 'relatively wide and relatively narrow slats alternately arranged and pivoted together by means including inner and outer flexible sheets adhered to opposite faces of each of the slats, means securing every [other one of said narrow :slats to intermediate points of each lazytongs, each of :said wide slats being a substantially flat sheet-like multiply structure and comprised of one layer of thin walled sheet steel stock to increase the frequency averaged sound isolating characteristics of the door by at least 4 db, and vertically extended pads of reiliently compressible fibrous sound insulating material mounted exteriorly in flush relation on the inner cover sheets at locations overlying and substantially masking thewide slats, said pads being of a thickness somewhat greater than one half the width of the narrow slats to increase the frequency averaged sound isolating characteristics of the door by at least another 4 7, db and to undergo yieldable compression when the door is folded to maintain substantially the same stacking ratio.

6. In an accordion type folding door having a pair of end posts that define opposite vertical end edges of the door, upper and lower extensible and collapsible lazytongs connecting said posts, foldable cover means disposed along opposite sides of said lazytongs and connected at opposite ends to the respective posts, flexible sealing skirts attached to and projecting from the upper and lower edges of the cover means, each cover means including a plurality of vertically elongated closely side-by-side disposed relatively wide and relatively narrow slats alternately arranged and pivoted together by rneans including inner and outer flexible sheets adhered to opposite faces of each of the slats, means securing every other one of said narrow slats to intermediate points of each lazytongs, each of said wide slats being a substantially flat sheet-like multi-ply structure and comprised of one layer of thin walled sheet steel stock provided with a full height bent portion to increase the anti-vibration rigidity of the wide slats and increase the frequency averaged sound isolating characteristics of the entire door, and vertically extended pads of resiliently compressible fibrous sound insulating material mounted exteriorly in flush relation on the inner cover sheets at locations overlying and substantially masking the wide slats, said pads being of a thickness somewhat greater than one half the width of the narrow slats to increase the frequency averaged sound isolating characteristics of the door by at least another 4 db and to undergo yieldable compression when the door is folded to maintain substantially the same stacking ratio.

7. An arrangement in accordance with claim 6 and wherein said pads are /2 inch thick and of a density of /2 pound per cubic foot, said sheet steel stock is 24 gauge thickness and said wide slats are at least five times as wide as the narrow slats such that the folding door exhibits sound isolating characteristics equivalent to that of a concrete block wall.

References Cited by the Examiner UNITED STATES PATENTS 2,068,977 1/1937 Dodge 236 2,782,845 2/1957 Johnson 16084 3,082,817 3/1963 Merrill 160-84 X FOREIGN PATENTS 445,690 1/1949 Italy.

HARRISON R. MOSELEY, Primary Examiner. 

1. IN AN ACCORDION TYPE FOLDING DOOR HAVING A PAIR OF END POSTS THAT DEFINE OPPOSITE VERTICAL END EDGES OF THE DOOR, UPPER AND LOWER EXTENSIBLE AND COLLAPSIBLE LAZYTONGS CONNECTING SAID POSTS, FOLDABLE COVER MEANS DISPOSED ALONG OPPOSITE SIDES OF SAID LAZYTONGS AND CONNECTED AT OPPOSITE ENDS TO THE RESPECTIVE POSTS, FLEXIBLE SEALING SKIRTS ATTACHED TO AND PROJECTING FROM THE UPPER AND LOWER EDGES OF THE COVER MEANS, EACH COVER MEANS INCLUDING A PLURALITY OF VERTICALLY ELONGATED CLOSELY SIDE-BY-SIDE DISPOSED RELATIVELY WIDE AND RELATIVELY NARROW SLATS ALTERNATELY ARRANGED AND PIVOTED TOGETHER BY MEANS INCLUDING INNER AND OUTER FLEXIBLE SHEETS ADHERED TO OPPOSITE FACES OF EACH OF THE SLATS, MEANS SECURING EVERY OTHER ONE OF SAID NARROW SLATS TO INTERMEDIATE POINTS OF EACH LAZYTONGS, EACH OF SAID WIDE SLATS BEING A SUBSTANTIALLY FLAT SHEET-LIKE STRUCTURE, AND VERTICALLY EXTENDED PADS OF LOW DENSITY RESILIENTLY COMPRESSIBLE FIBROUS SOUND SINSULATING MATERIAL MOUNTED EXTERIORLY IN FULL SURFACED FLUSH CONTACTING RELATION AGAINST THE INNER COVER SHEETS AT LOCATIONS OVERLYING AND SUBSTANTIALLY MASKING THE WIDE SLATS, SAID PADS BEING OF A THICKNESS SOMEWHAT GREATER THAN ONE HALF THE WIDTH OF THE NARROW SLATS TO INCRASE THE FREQUENCY SOUND ISOLATING CHARACTERISTICS OF THE DOOR BY AT LEAST 4 DB AND TO UNDERGO YIELDABLE COMPRESSION WHEN THE DOOR IS FOLDED TO MAINTAIN SUBSTANTIALLY THE SAME STACKING RATIO. 